[GHC] #16114: strange "instance .. => .. => .. where ..."

[GHC]

#16114: strange "instance .. => .. => .. where ..."
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        Reporter:  j.waldmann        |                Owner:  (none)
            Type:  bug               |               Status:  closed
        Priority:  normal            |            Milestone:  8.8.1
       Component:  Compiler          |              Version:  8.6.3
      Resolution:  fixed             |             Keywords:
Operating System:  Unknown/Multiple  |         Architecture:
                                     |  Unknown/Multiple
 Type of failure:  None/Unknown      |            Test Case:
                                     |  rename/should_fail/T16114
      Blocked By:                    |             Blocking:
 Related Tickets:                    |  Differential Rev(s):
       Wiki Page:                    |  https://gitlab.haskell.org/ghc/ghc/merge_requests/92
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Comment (by Ryan Scott <ryan.gl.scott@…>):

 In [changeset:"83a22066fbe136e4a984e8c90c1d3fd72b6ec4b9/ghc"
 83a22066/ghc]:
 {{{
 #!CommitTicketReference repository="ghc"
 revision="83a22066fbe136e4a984e8c90c1d3fd72b6ec4b9"
 Fix #16114 by adding a validity check to rnClsInstDecl
 }}}

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Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/16114#comment:9>
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